Oral solutions comprising lisdexamfetamine salts

ABSTRACT

Oral pharmaceutical solution comprising a pharmaceutically acceptable salt of lisdexamfetamine, and a pharmaceutically acceptable aqueous carrier comprising a buffer and a cosolvent selected from the group consisting of a glycol, a polyol, and a mixture thereof, wherein the pH of the solution is from 5.5 to 9.0. The oral pharmaceutical solution presents excellent physicochemical stability, even under alkaline conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 U.S. National Phase of InternationalApplication No. PCT/EP2020/060777, filed Apr. 16, 2020, which claimspriority to European Patent Application No. 19386059.0, filed Dec. 30,2019. The entire disclosures of the above applications are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to oral pharmaceutical solutionscomprising a pharmaceutically acceptable salt of lisdexamfetamine.

BACKGROUND OF THE INVENTION

Lisdexamfetamine or L-lysine-d-amfetamine (LDX; formerly NRP-104),(2S)-2,6-diamino-N-[(1S)-1-methyl-2-phenylethyl] hexanamidedimethanesulfonate) was first disclosed in U.S. Pat. No. 7,105,486.

Lisdexamfetamine has the following structure.

Lisdexamfetamine, sold under the brand names Elvanse® (DK, GB, SE),Tyvense® (IE), Venvanse® (BR), Vyvanse® (US, CA) among others, is amedication that is used to treat attention deficit hyperactivitydisorder (ADHD) in people over the age of six as well as for moderate tosevere binge eating disorder in adults.

Lisdexamfetamine is a pro-drug of dexamfetamine and containsD-amfetamine covalently linked to the essential amino acid L-lysine. Itlacks stimulant properties but is hydrolyzed in the gut wall to released-amfetamine. As it is an inactive material, it cannot be taken nasally,intravenously or in any other way b achieve an illicit stimulant effect.Furthermore, the metabolic hydrolysis of the pro-drug takes some timeand as such the formulation has an element of in-built controlledrelease notwithstanding that the product may contain only excipientsemployed in immediate release dosage forms. The product can deliverdexamfetamine over a period of about 8 hours and so it is useful totreat ADHD in paediatric populations (aged 6 to 12), but the extent ofits duration is not considered to be sufficient to treat adolescent andadult populations having much longer active days.

Lisdexamfetamine is currently commercially available only as 10, 20, 30,40, 50, 60 and 70 hard capsules or chewable tablets. Each capsule orchewable tablet contains 10, 20, 30, 40, 50, 60 or 70 mglisdexamfetamine dimesylate, equivalent to 5.8 mg, 11.6 mg, 17.3 mg,23.1 mg, 28.9 mg or 34.7 mg lisdexamfetamine, respectively.

Lisdexamfetamine dimesylate has the following structure.

Although oral solid dosage forms such as capsules are very popular forreasons that are mainly due to ease of management, for certain users(e.g. children) these forms are not necessarily a convenient option,especially due to difficulty in swallowing these forms. This lack ofconvenience results in high incidence of non-compliance and ineffectivetherapy.

Moreover, the Patient Information Leaflet (PIL) of Vyvanse®& Elvanse®discloses a dosing scheme for children over 6 years of age according towhich the dosage should be individualised according to the therapeuticneeds and response of the patient, while careful dose titration isnecessary at the start of treatment with Vyvanse® or Elvanse®. Theconcept of tailored treatment sets as prerequisite pharmaceutical forms,such as oral solutions, that enable dose fractioning.

According to WO 2006/121552, lisdexamfetamine can be alternativelyformulated as an aqueous solution, or a sterile composition.Compositions in these cases may be stored in freeze-dried form and maybe associated with a stabilizing agent such as a carbohydrate. In use,the composition may be deployed in an aqueous solution containing salts,e.g., NaCl, detergents such as sodium dodecyl sulfate (SDS), and othercomponents. Furthermore, according to this patent documentlisdexamfetamine may be formulated as liquid dispersion for oraladministration, for example as a syrup, emulsion, or suspension.However, no specific liquid based compositions are described in WO2006/121552.

There are a number of challenges surrounding the development of liquidbased formulations such as stability and solubility not adequatelyelaborated in the prior art. In fact, active pharmaceutical agents inliquid forms are more susceptible to chemical and physical instabilitythan in the solid state. In addition to the solubility, the activepharmaceutical agent needs to be physically and chemically stable in theoral solution. Trace amounts of impurities from active pharmaceuticalagents or excipients and the pH of the solution may cause thedegradation of the active pharmaceutical agent and this may cause anincrease in instability when the solution is consistently introducedinto the atmosphere.

Although lisdexamfetamine acid addition salts, such as lisdexamfetaminedimesylate and lisdexamfetamine hydrochloride are very soluble in water,the desire for the development of an oral solution of a lisdexamfetaminesalt is complicated by the fact that the molecule degrades significantlyat basic (alkaline) and oxidative conditions.

According to Carlos G. et. al., “Assessment of lisdexamfetaminedimesylate stability and identification of its degradation product byNMR spectroscopy” Drug Dev Ind Pharm. 2019 January, althoughlisdexamfetamine dimesylate degrades at both acidic and alkalineconditions, it is more hydrolysis-susceptible under alkaline conditions.

According to Shenghua G. et. al., “Identification, characterization andquantification of process-related and degradation impurities inlisdexamfetamine dimesylate: identification of two new compounds”,molecules. 2018 December; 23(12): 3125, lisdexamfetamine can produce atleast Imp-A, Imp-B or Imp-C in alkaline conditions, whereas at leastImp-M is produced under oxidative conditions.

The main known degradation impurities of lisdexamfetamine are shownbelow.

Technically, the biggest challenge is the development of liquid basedformulations. using stabilizing excipients with low toxicity in thelowest feasible concentrations without compromising the stability of theformulations. In other words, the low concentrations of stabilizingexcipients may contribute to reducing the potential for toxicologicaleffects, but they may be insufficient for achieving the required levelof physicochemical stability.

The present invention overcomes the problems of the prior art andprovides an oral pharmaceutical solution, comprising a pharmaceuticallyacceptable salt of lisdexamfetamine, which exhibits excellent stabilityand extended lifetime.

SUMMARY OF INVENTION

The present invention provides a physicochemically stable oralpharmaceutical solution comprising a pharmaceutically acceptable salt oflisdexamfetamine.

The oral pharmaceutical solution according to the invention comprises apharmaceutically acceptable salt of lisdexamfetamine, and apharmaceutically acceptable aqueous carrier comprising a buffer and acosolvent selected from the group consisting of a glycol, a polyol, anda mixture thereof, wherein the pH of the solution is from 5.5 to 9.0.

The oral pharmaceutical solution according to the invention presentsexcellent physicochemical stability.

The present invention has the advantage that it provides a stable oralpharmaceutical solution of a pharmaceutically acceptable salt oflisdexamfetamine, by inhibiting hydrolysis and oxidation that typicallyoccur after extended storage.

Further to that, oral solutions of the present invention provide thebest alternative over conventional capsule or chewable tablet dosageforms. Apart from achieving better patient compliance, oral solutions ofthe present invention offer unique advantages such as more reproduciblebioavailability and an option of a flexible dosing regimen based on bodyweight or body surface area.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a stable oral pharmaceutical solutioncomprising a pharmaceutically acceptable salt of lisdexamfetamine inassociation with a pharmaceutically acceptable liquid carrier.

The term “stable” as used herein, refers to both physical and chemicalstability, wherein not more than 1.0% of total degradation impuritiesare formed on storage at 40° C. and 75% relative humidity over a periodof four weeks.

According to David W. Goodman, “Lisdexamfetamine dimesylate. The firstprodrug stimulant” Psychiatry (Edgmont). 2007 August; 4(8): 39-45, thepH solubility profile of lisdexamfetamine dimesylate in saturatedbuffered aqueous solutions (pH 1-13) was determined by a high-pressureliquid chromatography assay that was specific for lisdexamfetaminedimesylate. Lisdexamfetamine dimesylate was proved to be highly solublewithin a physiologically relevant pH range (pH 1-8). Its solubilityprofile was not affected by the pH of the solution, and increasing thepH from 8 to 13 resulted only in modest reductions in lisdexamfetaminedimesylate solubility.

Although lisdexamfetamine acid addition salts, such as lisdexamfetaminedimesylate are very soluble in water, the desire for the development ofan oral solution of a lisdexamfetamine salt is complicated by the factthat the molecule degrades significantly at alkaline and oxidativeconditions.

Unexpectedly, it has been found that the inclusion of commonantioxidants such as sodium metabisulfite and butylated hydroxyanisoleto oral solutions comprising a pharmaceutically acceptable salt oflisdexamfetamine did not actually prevent decomposition of the activeagent after storage.

Further to that, inclusion of certain additives commonly used asstabilizers in aqueous oral solutions, such as α-cyclodextrins,β-cyclodextrins and γ-cyclodextrins did not actually enhance thestability of lisdexamfetamine salts. The same applies to the inclusionof commonly used surfactants/stabilizers, such as sorbitan oleate esterand polyoxyethylene sorbitan monooleate, which also did not enhance thestability of lisdexamfetamine salts.

On the other hand, it has now been found that, although pharmaceuticallyacceptable salts of lisdexamfetamine are highly soluble in the pH rangeof 1 to 13, which means that there is no need of addition of acosolvent, their physicochemical stability in aqueous solutions issurprisingly enhanced by the addition of certain non-aqueous cosolventssuch as a glycol, or a polyol or a mixture thereof. Furthermore, it hasbeen found that the addition of such a cosolvent leads to a stable andhomogenous solution of a pharmaceutically acceptable salt oflisdexamfetamine, not only around neutral pH, but also in alkaline pH.This finding is unexpected since it does not apply to other cosolvents,commonly used in oral solutions. For example, the addition of diethyleneglycol monoethyl ether, or macrogol (15)-hydroxystearate does notenhance the stability of lisdexamfetamine salts in an aqueous solution.

The oral pharmaceutical solution according to the invention comprises apharmaceutically acceptable salt of lisdexamfetamine and apharmaceutically acceptable aqueous carrier comprising a buffer and acosolvent selected from the group consisting of a glycol, a polyol, anda mixture thereof, wherein the pH of the solution is from 5.5 to 9.0.

As used throughout this description and claims, a “glycol” may bepropylene glycol, polyethylene glycol or any other pharmaceuticallyacceptable polyalkylene glycol product such as those known in the art asthe “PEG” series, or mixtures thereof. Preferably, the glycol isselected from the group consisting of propylene glycol and low molecularweight polyethylene glycols i.e. liquid polyethylene glycols withaverage molecular weight lower than 600. More preferably, the glycol ispolyethylene glycol with average molecular weight lower than 600. Thisglycol provides the additional advantage of masking the bitter taste ofpharmaceutically acceptable salts of lisdexamfetamine.

As used throughout this description and claims, the term “polyol”(polyhydric alcohol) refers to pharmaceutical excipients containingmultiple hydroxyl groups. Although the term “polyol” includes sugaralcohols, it does not include sugars, i.e. carbohydrates, such assucrose, glucose, dextrose, fructose and galactose. Polyols aregenerally used as sweeteners and bulking agents. They occur naturally infoods and come from plant products such as fruits and berries. Typicalexamples of suitable polyols according to the invention are sugaralcohols such as, maltitol, glycerol, sorbitol, xylitol, erythritol,isomalt and lactitol, as well as polyvinyl alcohol. Some of thesepolyols, such as the sugar alcohols, impart a sweet taste to the overallsolution and act as a preservative. Preferably, the polyol is selectedfrom the group consisting of maltitol, glycerol, mannitol, sorbitol andxylitol. More preferably, the polyol is maltitol. Maltitol substantiallymasks the bitter taste of pharmaceutically acceptable salts oflisdexamfetamine as a result of its sweet taste and in addition, it isnon-cariogenic. Maltitol is used as a low-calorie sweetening agent, itis slowly absorbed and exhibits a low effect on blood glucose, whichmakes it more suitable for people. It is not metabolized by oralbacteria, so it does not promote tooth decay. It has an additionaladvantage in that crystallization is less likely to occur.

Any pharmaceutically acceptable system which acts as a buffer in the pHregion of the invention can be used in the oral pharmaceutical solution.Buffering agents may include but not limited to ascorbic acid, aceticacid, tartaric acid, citric acid monohydrate, sodium citrate, potassiumcitrate, acetic acid, sodium acetate, sodium hydrogen phosphate, sodiumdihydrogen phosphate, calcium hydrogen phosphate, calcium dihydrogenphosphate or mixtures thereof.

The oral pharmaceutical solution according to the invention may compriseany pharmaceutically acceptable salt of lisdexamfetamine such as2-hydroxyethanesulfonate, 2-naphthalenesulfonate,3-hydroxy-2-naphthoate, 3-phenylpropionate, acetate, adipate, alginate,amsonate, aspartate, benzenesulfonate, benzoate, besylate, bicarbonate,bisulfate, bitartrate, borate, butyrate, calcium edetate, camphorate,camphorsulfonate, camsylate, carbonate, citrate, clavulariate,cyclopentanepropionate, digluconate, dodecylsulfate, edetate, edisylate,estolate, esylate, ethanesulfonate, finnarate, gluceptate,glucoheptanoate, gluconate, glutamate, glycerophosphate,glycollylarsanilate, hemisulfate, heptanoate, hexafluorophosphate,hexanoate, hexylresorcinate, hydrabamine, hydrobromide, hydrochloride,hydroiodide, hydroxynaphthoate, iodide, isothionate, lactate,lactobionate, laurate, laurylsulphonate, malate, maleate, mandelate,mesylate, methanesulfonate, methylbromide, methylnitrate, methylsulfate,mucate, naphthylate, napsylate, nicotinate, nitrate, N-methylglucamineammonium salt, oleate, oxalate, palmitate, pamoate, pantothenate,pectinate, persulfate, phosphate, phosphateldiphosphate, picrate,pivalate, polygalacturonate, propionate, p-toluenesulfonate, saccharate,salicylate, stearate, subacetate, succinate, sulfate, sulfosaliculate,suramate, tannate, tartrate, teoclate, thiocyanate, tosylate,triethiodide, undecanoate, and valerate salts, and the like. Preferably,the oral pharmaceutical solution according to the invention compriseslisdexamfetamine dimesylate or lisdexamfetamine hydrochloride. Morepreferably, the oral pharmaceutical solution according to the inventioncomprises lisdexamfetamine dimesylate.

Preferably, the oral pharmaceutical solution according to the inventioncomprises from 1 mg/ml to 40 mg/ml of a pharmaceutically acceptable saltof lisdexamfetamine. More preferably, the solution comprises from 5mg/ml to 30 mg/ml of a pharmaceutically acceptable salt oflisdexamfetamine. Even more preferably, the solution comprises from 10mg/ml to 20 mg/ml of a pharmaceutically acceptable salt oflisdexamfetamine.

Preferably, the oral pharmaceutical solution according to the inventioncomprises from 5 mg/ml to 30 mg/ml of lisdexamfetamine dimesylate.

More preferably, the oral pharmaceutical solution according to theinvention comprises from 10 mg/ml to 20 mg/ml of lisdexamfetaminedimesylate.

Preferably, the total concentration of the cosolvent in the oralpharmaceutical solution according to the invention is from 5 to 300mg/ml. More preferably, the total concentration of the cosolvent is from50 mg/ml to 250 mg/ml. Even more preferably, the total concentration ofthe cosolvent is from 100 mg/ml to 200 mg/ml.

Preferably, the pH of the solution is from 6.0 to 8.5.

More preferably, the pH of the solution is from 6.5 to 8.0.

According to a preferred embodiment, the oral pharmaceutical solutionaccording to the invention comprises from 1 mg/ml to 40 mg/ml of apharmaceutically acceptable salt of lisdexamfetamine, and apharmaceutically acceptable aqueous carrier comprising a buffer, and acosolvent selected from the group consisting of a glycol a polyol, and amixture thereof, wherein the total concentration of the cosolvent isfrom 5 mg/ml to 300 mg/ml, wherein the pH of the solution is from 5.5 to9.0.

According to a more preferred embodiment, the oral pharmaceuticalsolution according to the invention comprises from 1 mg/ml to 40 mg/mlof a pharmaceutically acceptable salt of lisdexamfetamine, and apharmaceutically acceptable aqueous carrier comprising a buffer and acosolvent selected from the group consisting of maltitol, glycerol,mannitol, sorbitol, xylitol, propylene glycol, low molecular weightpolyethylene glycols, and a mixture thereof, wherein the totalconcentration of the cosolvent is from 5 mg/ml to 300 mg/ml, wherein thepH of the solution is from 5.5 to 9.0.

Preferably, the oral pharmaceutical solution according to the inventionis free of any antioxidant, such as sodium metabisulfite, butylatedhydroxyanisole, butylated hydroxytoluene, ethylenediamine tetraaceticacid, ascorbic acid, α-tocopherol, and propyl gallate.

The oral pharmaceutical solution according to the invention may alsooptionally contain additional excipients commonly used in preparing oralliquid compositions, such as antimicrobial preservatives, viscosityadjusting agents, sweeteners and flavouring agents.

Antimicrobial preservatives may include but not limited to sodiumbenzoate, benzoic acid, boric acid, sorbic acid and their salts thereof,benzyl alcohol, parahydroxy benzoic acids and their alkyl esters,methyl, ethyl and propyl parahydroxy benzoates and their salts ormixtures thereof.

Sweeteners may include but not limited to sucralose, aspartame,acesulfame-K, thaumatin, mogroside, saccharin and salts thereof, sodiumcyclamate, glucose, sucrose, lactose, fructose, erythritol,glycyrrhizin, monosodium glycyrrhizinate, monoamonium glycyrrhizinate,dextrose or mixtures thereof.

Flavouring agents used in the oral pharmaceutical solution according tothe invention may include but not limited to fruit flavours such asorange, banana, strawberry, cherry, wild cherry, lemon and the like andother flavourings, such as cardamom, anise, mint, menthol, vanillin,bubble gum or mixtures thereof.

The oral pharmaceutical solution according to the invention ispreferably supplied as a multidose preparation. Each dose from amultidose container, such as amber type III glass 50 or 100 ml bottlessealed with child resistant, tamper evident screw caps, can beadministered by means of a device suitable for measuring the prescribedvolume. The device is usually a spoon or a cup for volumes of 5 ml ormultiples thereof, or an oral syringe for other volumes.

The oral pharmaceutical solution of the present invention may beprepared using methods well known in the art and using regularmanufacturing equipment.

For example, it may be prepared using the following process:

The active substance and the excipients are weighed. Purified water isadded into a vessel. The pharmaceutically acceptable salt oflisdexamfetamine and the cosolvent, are successively dissolved intopurified water under stirring. A pH buffer solution, prepared in adifferent vessel, is added under continuous stirring until thepharmaceutically acceptable salt of lisdexamfetamine is completelydissolved. Preservative, if present, is also added under continuousstirring until complete dissolution. Flavour and the remainingexcipients, if present, are successively added under continuousstirring, until complete dissolution. The pH of the solution is adjustedwith a quantity of the buffer solution to the desired value. Finally,the volume is adjusted with purified water.

The final solution is optionally filtered over a 10 μm filter, andfilled preferably in light-protective containers, such as amber type IIIglass 50 or 100 ml bottles sealed with child resistant, tamper evidentscrew caps.

EXAMPLES Example 1

The purpose of this experiment was to evaluate the influence of commonantioxidants on the stability of lisdexamfetamine dimesylate solutions.

These lisdexamfetamine dimesylate compositions were prepared in thefollowing manner:

In the main vessel, 80% of the amount of purified water was transferredunder magnetic stirring. The amounts of citric acid and sodium citratewere slowly added until complete dissolution. The amount oflisdexamfetamine dimesylate was slowly added in the main vessel understirring until complete dissolution. The pH value of the solution wasmeasured and adjusted, if needed, at the optimum value. Purified waterwas added to the final batch size.

Storage conditions of temperature (4000) and relative humidity (75%)applied for a period of four weeks. Quantification of lisdexamfetaminedimesylate and its impurities, in the compositions prepared, wasperformed by HPLC.

TABLE 1 Compositions Trial 1 Trial 2 Trial 3 Function Component mg/mlAPI Lisdexamfetamine dimesylate 10   10 10   Antioxidant Sodiummetabisulfite — 1 — BHA — — 0.5 buffering agent Citric acid monohydrate2.0 2.0 2.0 Sodium Citrate dihydrate 0.9 0.9 0.9 pH adjustment agentCitric acid (10% w/v))/ Qs to pH 6.5 Qs to pH 6.5 Qs to pH 6.5 Sodiumcitrate (10% w/v) Diluent PW Qs to 1 mL

TABLE 2 Stability results Parameter Trial 1 Trial 2 Trial 3 T = 0 pH6.46 6.40 6.45 Assay n/a 97.3% 98.6% Impurities Not Detected RRT 0.46:0.02% Not Detected RRT 0.66: 0.01% RRT 0.94: 005% RRT 0.96: 0.03% Totalimpurities Not Detected 0.11% Not Detected 40° C./75% 4 weeks pH 6.466.30 6.40 Assay n/a 95.0% 95.8% Impurities Dxtroamfet: 0.02% Dxtroamfet:0.02% Dxtroamfet: 0.02% D-Ldxamfet: 0.04% D-Ldxamfet: 0.05% D-Ldxamfet:0.05% RRT 0.44: 0.04% RRT 0.44: 0.04% RRT 0.44: 0.04% RRT 0.45: 0.08%RRT 0.45: 0.10% RRT 0.45: 0.11% RRT 0.47: 0.07% RRT 0.47: 0.07% RRT0.47: 0.06% RRT 0.69: 0.04% RRT 0.49: 0.02% RRT 0.49: 0.02% RRT 0.70:0.07% RRT 0.64: 0.01% RRT 0.64: 0.01% RRT 0.72: 0.13% RRT 0.69: 0.04%RRT 0.69: 0.05% RRT 0.83: 0.01% RRT 0.70: 0.07% RRT 0.70: 0.06% RRT0.94: 0.22% RRT 0.72: 0.12% RRT 0.72: 0.11% RRT 0.97: 0.19% RRT 0.73:0.01% RRT 0.73: 0.02% RRT 1.08: 0.04% RRT 0.75: 0.01% RRT 0.94: 0.33%RRT 1.09: 0.01% RRT 0.83: 0.01% RRT 0.97: 0.18% RRT 1.14: 0.05% RRT0.94: 0.33% RRT 1.08: 0.04% RRT 0.97: 0.18% RRT 1.09: 0.01% RRT 1.08:0.04% RRT 1.14: 0.02% RRT 1.09: 0.01% RRT 1.14: 0.05% Total impurities  1.01% 1.18% 1.13% Dxtroamfet: Dextroamfetamine D-Ldxamfet:D-Lisdexamfetamine

Surprisingly it was found that the addition of antioxidants did notprevent decomposition of the active agent after storage. Instead, thedecomposition was very significant. Furthermore, inclusion of 200 mg/mlof diethylene glycol monomethyl ether to the compositions of Table 1 didnot enhance the stability of the active agent.

Example 2

The purpose of this experiment was to evaluate the influence of pHbetween 2.5 and 5.5 on the stability of lisdexamfetamine dimesylatesolutions, when maltitol is used as cosolvent.

These compositions were prepared in the following manner:

In the main vessel, 80% of the amount of purified water was transferredunder magnetic stirring. The amounts of citric acid and sodium citratewere slowly added under stirring until complete dissolution. In the mainvessel, the amount of lisdexamfetamine dimesylate and maltitol wasslowly added under stirring until complete dissolution. The pH value ofthe solution was measured and adjusted, if needed, at the optimum value.Purified water was added to the final batch size.

Storage conditions of temperature (40° C.) and relative humidity (75%)applied for a period of four weeks. Quantification of lisdexamfetaminedimesylate and its impurities, in the compositions prepared, wasperformed by HPLC.

TABLE 2a Compositions Trial 1′ Trial 2′ Trial 3′ Trial 4′ (pH ~2.5) (pH~3.5) (pH ~4.5) (pH ~5.5) Function Component mg/ml Cosolvent Maltitol100 100 100 100 API Lisdexamfetamine dimesylate 10 10 10 10 Bufferingagent Citric acid monohydrate 3.0 2.0 1.0 0.8 Sodium Citrate dihydrate0.1 0.9 1.2 3.0 pH adjustment agent Citric acid (10% w/v))/ Qs to pH Qsto pH Qs to pH Qs to pH Sodium citrate (10% w/v) 2.5 3.5 4.5 5.5 DiluentPW Qs to 1 mL

TABLE 2b Stability study results Trial 1′ Trial 2′ Trial 3′ Trial 4′Parameter (pH ~2.5) (pH: ~3.5) (pH: ~4.5) (pH ~5.5) T = 0 pH 2.8 3.7 4.75.7 Assay 101.1% 97.0% 96.7% 103.8% Impurities Not Detected Not DetectedNot Detected Not Detected Total impurities Not Detected Not Detected NotDetected Not Detected 40° C./75% 2 weeks pH 2.8 3.7 4.7 5.7 Assay NA NANA NA Dxtroamfet: 0.14% 0.39% 0.28% 0.03% RRT 0.68: 0.18% 0.68% 0.84%0.26% RRT 0.72: 0.35% 1.2% 1.4% 0.41% RRT 0.75: Not detected 0.06% 0.09%0.05% Total impurities 0.67% 2.3% 2.6% 0.75% 40° C./75% 4 weeks pH 2.83.7 4.7 5.7 Assay 100.4% 95.7% 94.3% 102.1% Dxtroamfet: 0.34% 0.93%0.73% 0.06% RRT 0.68: 0.36% 1.2% 1.5% 0.57% RRT 0.72: 0.46% 1.6% 2.4%0.79% RRT 0.75 Not detected 0.07% 0.11% 0.06% Total impurities 1.2% 3.8%4.7% 1.5% Dxtroamfet: Dextroamfetamine

From this study, it is concluded that even in the presence of maltitolas cosolvent, control of pH is critical for the stability oflisdexamfetamine dimesylate and that pH values up to 5.5 do not providethe desired stability of lisdexamfetamine dimesylate.

Example 3

The purpose of this experiment was also to evaluate the influence of pHbetween 6 and 8.5 on the stability of lisdexamfetamine dimesylatesolutions, when maltitol is used as cosolvent.

These lisdexamfetamine dimesylate solutions were prepared as describedin example 2.

Storage conditions of temperature (40° C.) and relative humidity (75%)applied for a period of four weeks. Quantification of lisdexamfetaminedimesylate and its impurities, in the compositions prepared, wasperformed by HPLC.

TABLE 3a Compositions Trial 5′ Trial 6′ Trial 7′ (pH ~6.0) (pH ~6.5) (pH~6.5) Function Component mg/ml API Lisdexamfetamine dimesylate  10  10 10 Cosolvent Maltitol 100 100 100 pH adjustment agent Citric acid (10%w/v))/ Qs to pH 6.0 Qs to pH 6.5 — Sodium citrate (10% w/v) Disodiumhydrogen — — Qs to pH 6.5 phosphate(10% w/v)/Sodium dihydrogen phosphate(10% w/v) Diluent Purified water Qs to 1 mL

TABLE 3b Compositions Trial 8′ Trial 9′ Trial 10′ Function Component (pH~7.0) (pH ~7.5) (pH ~8.5) API Lisdexamfetamine dimesylate 10 10 10Cosolvent Maltitol 100  100  100  pH adjustment agent Disodium hydrogenphosphate(10% w/v)/ — — — Sodium dihydrogen phosphate (10% w/v) Qs to pH7.0 Qs to pH 7.5 Qs to pH 8.5 Diluent Purified water Qs to 1 mL

TABLE 3c Stability results Trial 5′ Trial 6′ Trial 7′ Parameter (pH~6.0) (pH ~6.5) (pH ~6.5) T = 0 pH 5.98 6.46 6.46 Assay 102.3% 104.3%97.4% Impurities Not Detected Not Detected Not Detected Total impuritiesNot Detected Not Detected Not Detected 40° C./75% 4 weeks pH 5.94 6.456.46 Assay 101.2% 104.8% 97.9% Impurities D-Ldxamfet: 0.03% D-Ldxamfet:0.06% RRT 0.70: 0.13% RRT 0.70: 0.03% RRT 0.72: 0.21% RRT 0.72: 0.05%RRT 0.75: 0.02% Total impurities 0.39% 0.08% 0.06%

TABLE 3d Stability results Trial 8′ Trial 9′ Trial 10′ Parameter (pH~7.0) (pH ~7.5) (pH ~8.5) T = 0 pH 6.95 7.46 8.56 Assay 100.8% 99.6%99.3% Impurities ND RRT 0.46: 0.01% RRT 0.46: 0.02% Total impurities ND0.01% 0.02% 40° C./75% 4 weeks pH 6.94 7.46 8.48 Assay 101.3% 100.5%99.0% Impurities D-Ldxamfet: 0.11% Dxtroamfet: 0.01% Dxtroamfet: 0.01%D-Ldxamfet: 0.18% D-Ldxamfet: 0.16% RRT 0.72: 0.01% RRT 0.75: 0.02%Total impurities 0.11% 0.17% 0.22%

From this study, it is surprisingly concluded that in the presence ofmaltitol as cosolvent the stability of lisdexamfetamine dimesylate issignificantly increased when the pH of the solution is at least 6.Moreover, excellent stability of lisdexamfetamine dimesylate is achievedeven under alkaline conditions.

Example 4

Preferred liquid compositions of lisdexamfetamine dimesylate.

These lisdexamfetamine dimesylate compositions were prepared in thefollowing manner:

Purified water was added into a vessel. Lisdexamfetamine dimesylate andthe cosolvent(s), are successively dissolved into purified water understirring. A pH buffer solution, prepared in a different vessel, wasadded under continuous stirring until lisdexamfetamine dimesylate wascompletely dissolved. Preservative, was also added under continuousstirring until complete dissolution. The flavour was then added undercontinuous stirring, until complete dissolution. The pH of the solutionwas adjusted with a quantity of the buffer solution to the desiredvalue. Finally, the volume was adjusted with purified water.

Storage conditions of temperature (40° C.) and relative humidity (75%)applied for a period of four weeks. Quantification of lisdexamfetaminedimesylate and its impurities, in the compositions prepared, wasperformed by HPLC.

TABLE 4a preferred compositions according to the present inventionComposition I Composition II Composition III mg/ml Active ingredientLisdexamfetamine dimesylate 10 10 10 Excipients Maltitol 50 — —Propylene glycol — 200 — PEG-400 — — 100 Sodium benzoate 0.1 0.1 0.1Flavour mint 0.5 0.5 0.5 Purified water q.s. 1 ml q.s. 1 ml q.s. 1 mlPhosphate buffer solution pH: 6.5 pH: 6.5 pH: 6.5

TABLE 4b preferred compositions according to the present inventionComposition IV Composition V Composition VI mg/ml Active ingredientLisdexamfetamine dimesylate 10 10 10 Excipients Glycerol 100 — —Sorbitol — 100 — Xylitol — 100 150 Sodium benzoate 0.1 0.1 0.1 Flavourmint 0.5 0.5 0.5 Purified water q.s. 1 ml q.s. 1 ml q.s. 1 ml Phosphatebuffer solution pH: 6.5 pH: 6.5 pH: 6.5

TABLE 4c Stability results Parameter Composition I Composition IIComposition III T = 0 pH 6.48 6.46 6.46 Assay 102.3% 101.3% 99.9%Impurities ND ND ND Total impurities ND ND ND pH 6.46 6.45 6.46 Assay101.2% 100.8% 99.6% 40° C./75% 4 weeks Impurities D-Ldxamfet: 0.03%D-Ldxamfet: 0.06% RRT 0.70: 0.13% RRT 0.70: 0.03% RRT 0.72: 0.11% RRT0.72: 0.05% RRT 0.75: 0.02% Total impurities 0.29% 0.08% 0.06%

TABLE 4d Stability results Parameter Composition IV Composition VComposition VI T = 0 pH 6.48 6.46 6.46 Assay 100.3% 100.9% 99.8%Impurities ND ND ND Total impurities ND ND ND 40° C./75% 4 weeks pH 6.466.45 6.46 Assay 99.2% 100.3% 99.6% Impurities D-Ldxamfet: 0.03%D-Ldxamfet: 0.03% Dxtroamfet: 0.02% RRT 0.72: 0.09% RRT 0.72: 0.08%D-Ldxamfet: 0.06% RRT 0.75: 0.12% RRT 0.75: 0.04% RRT 0.72: 0.09% RRT0.75: 0.06% RRT 0.79: 0.05% Total impurities 0.24% 0.15% 0.28%Dxtroamfet: Dextroamfetamine D-Ldxamfet: D-Lisdexamfetamine

The invention claimed is:
 1. Oral pharmaceutical solution comprisingfrom 1 mg/ml to 40 mg/ml of a pharmaceutically acceptable salt oflisdexamfetamine and a pharmaceutically acceptable aqueous carriercomprising a buffer and a cosolvent selected from the group consistingof a glycol, a polyol and a mixture thereof, wherein the pH of thesolution is from 5.5 to 9.0.
 2. Oral pharmaceutical solution accordingto claim 1, wherein the solution is free of any antioxidant.
 3. Oralpharmaceutical solution according to claim 1, wherein the solution isfree of an antioxidant selected from the group consisting of sodiummetabisulfite, butylated hydroxy anisole, butylated hydroxytoluene,ethylenediamine tetraacetic acid, ascorbic acid, α-tocopherol, andpropyl gallate.
 4. Oral pharmaceutical solution according to claim 1,wherein the cosolvent is selected from the group consisting of maltitol,glycerol, mannitol, sorbitol, xylitol, propylene glycol, low molecularweight polyethylene glycol and a mixture thereof.
 5. Oral pharmaceuticalsolution according to claim 1, wherein the cosolvent is selected fromthe group consisting of maltitol and low molecular weight polyethyleneglycol.
 6. Oral pharmaceutical solution according to claim 1, whereinthe cosolvent is maltitol.
 7. Oral pharmaceutical solution according toclaim 1, wherein the total concentration of the cosolvent is from 5mg/ml to 300 mg/ml.
 8. Oral pharmaceutical solution according to claim1, wherein the total concentration of the cosolvent is from 50 mg/ml to250 mg/ml.
 9. Oral pharmaceutical solution according to claim 1, whereinthe total concentration of the cosolvent is from 100 mg/ml to 200 mg/ml.10. Oral pharmaceutical solution according to claim 1, wherein the pH ofthe solution is from 6.0 to 8.5.
 11. Oral pharmaceutical solutionaccording to claim 1, wherein the pH of the solution is from 6.5 to 8.0.12. Oral pharmaceutical solution according to claim 1, wherein theconcentration of the pharmaceutically acceptable salt oflisdexamfetamine is from 5 mg/ml to 30 mg/ml.
 13. Oral pharmaceuticalsolution according to claim 1, wherein the concentration of thepharmaceutically acceptable salt of lisdexamfetamine is from 10 mg/ml to20 mg/ml.
 14. Oral pharmaceutical solution according to claim 1, whereinthe pharmaceutically acceptable salt of lisdexamfetamine is selectedfrom the group consisting of lisdexamfetamine dimesylate andlisdexamfetamine hydrochloride.
 15. Oral pharmaceutical solutionaccording to claim 1, wherein the pharmaceutically acceptable salt oflisdexamfetamine is lisdexamfetamine dimesylate.